see https://github.com/doctrine/phpcr-odm/wiki/References-and-related
looks like uwe is working on that one: https://github.com/uwej711/phpcr-odm/tree/parent_annotation
can we close this one?
https://github.com/doctrine/phpcr-odm/pull/66
see https://github.com/doctrine/phpcr-odm/wiki/References-and-related